[R] date.mdy in date package

[Spencer Graves]

	  Evidently, your 'trimmed_dates' was NOT a "a Julian date value, as 
returned by 'mdy.date()', number of days since 1/1/1960."
	
	  My standard references for this kind of thing are the "zoo" vignette 
and the R News article, Gabor Grothendieck and Thomas Petzoldt. R help 
desk: Date and time classes in R. R News, 4(1):29-32, June 2004 
(www.r-project.org -> Documentation:  Newsletter).  For more on 
vignettes and "zoo" in particular, see 
"http://finzi.psych.upenn.edu/R/Rhelp02a/archive/67006.html".

	  With my limited knowledge of date-time formates, I might approach 
your problem as follows:


 > Lines <-
+ "1  1/2/2003    2  1/3/2003    3  1/6/2003    4  1/7/2003    5 
1/8/2003    6  1/9/2003    7  1/10/2003    8  1/13/2003    9  1/14/2003"
 > (DF <- read.table(textConnection(Lines)))
   V1       V2 V3       V4 V5       V6 V7       V8 V9      V10 V11 
V12 V13
1  1 1/2/2003  2 1/3/2003  3 1/6/2003  4 1/7/2003  5 1/8/2003   6 
1/9/2003   7
         V14 V15       V16 V17       V18
1 1/10/2003   8 1/13/2003   9 1/14/2003
 > (Dates <- sapply(DF[2*(1:9)], as.character))
          V2          V4          V6          V8         V10         V12
  "1/2/2003"  "1/3/2003"  "1/6/2003"  "1/7/2003"  "1/8/2003"  "1/9/2003"
         V14         V16         V18
"1/10/2003" "1/13/2003" "1/14/2003"
 > (Dates. <- strptime(Dates, "%m/%d/%Y"))
[1] "2003-01-02" "2003-01-03" "2003-01-06" "2003-01-07" "2003-01-08"
[6] "2003-01-09" "2003-01-10" "2003-01-13" "2003-01-14"
 > class(Dates.)
[1] "POSIXt"  "POSIXlt"
 > names(Dates.)
[1] "sec"   "min"   "hour"  "mday"  "mon"   "year"  "wday"  "yday"  "isdst"
 >
	  Thus, the 'POSIXlt' format is similar to the output of 'date.mdy', 
except that it has other attributes, which you could ignore.  Getting 
"month / days with leading zeros" is a formatting issue.  If you still 
can't figure that out after studying the Grothendieck and Petzoldt 
article and the zoo vignette, please submit another post.

	  hope this helps.
	  Spencer Graves

Brian Scholl wrote:
> I'm having a problem with output from date.mdy in the date package. 
>    
>   Goal: to take a long vector of dates of the form "01/22/99" and extract values month="01", day="22", year="1999".  
>    
>   I am providing the vector of class dates in the attached file to date.mdy: 
>    
>   > mdy_dates<-date.mdy(trimmed_dates)
>    
>   The first few obs of the attached vector of dates are: 
>               1  1/2/2003    2  1/3/2003    3  1/6/2003    4  1/7/2003    5  1/8/2003    6  1/9/2003    7  1/10/2003    8  1/13/2003    9  1/14/2003
>    
>   I am expecting to get a list with vectors for the day, month, and year.  The function appears to spit out the format I expect (though I would like months/days with leading zeros) but incorrect values, But what I get in the first few lines is something like: 
>    
>   > mdy_dates
> $month
>   [1]  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  2  2  2
>  [26]  2  2  2  2  2  2  2  2  2  2  2  2  2  2  2  2  2  3  3  3  3  3  3  3  3
>  [51]  3  3  3  3  3  3  3  3  3  3  3  3  3  3  4  4  4  4  4  4  4  4  4  4  4
> $day
>   [1]  1  2  5  6  7  8  9 12 13 14 15 16 19 20 21 22 23 26 27 28 29 30  2  3  4
>  [26]  5  6  9 10 11 12 13 16 17 18 19 20 23 24 25 26 27  2  3  4  5  6  9 10 11
>  [51] 12 13 16 17 18 19 20 23 24 25 26 27 30 31  1  2  3  6  7  8  9 10 13 14 15
> $year
>   [1] 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993
>  [16] 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993
>  [31] 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993 1993
> 
>   So: The first day of my list of dates is Jan 2, 2003, but in the list output the first date is Jan 1, 1993.  Have I incorrectly formatted my input, or is there some other problem? 
>    
>   Thanks in advance. 
> 
>  __________________________________________________
> 
> 
> 
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